Microelectromechanical systems (MEMS) are very small movable mechanical structures built using standard semi-conductor processes. MEMS can be provided as actuators, which are very useful in many applications. These actuators are typically having a length of a few hundreds of microns, sometimes with only a few tens of microns in width. A MEMS actuator is usually configured and disposed in a cantilever fashion. It thus has an end attached to a substrate and an opposite free end which is movable between at least two positions, one being a neutral position and the others being deflected positions.
The most common actuation mechanisms used in the industry are electrostatic, magnetic, piezo and thermal. The actuation mechanism discussed herein is of a thermal type. The deflection of a thermal MEMS actuator results from a potential being applied between a pair of terminals, called “anchor pads”, which potential causes a current flow elevating the temperature of the structure. This ultimately causes a part thereof to contract or elongate, depending on the material being used.
One possible use for MEMS actuators is to configure them as switches. These switches are made of at least one actuator. In the case of multiple actuators, they are operated in sequence so as to connect or release one of their parts to a similar part on the other. The actuator or actuators can be single hot arm actuators or double hot arm actuators, depending on the design. Other kinds of actuators exist as well, including some with more than two hot arm members. These actuators form a switch which can be selectively opened or closed using a control voltage applied at corresponding anchor pads on each actuator.
Because they are extremely small, each actuator being about a few hundreds of microns in length and a few tenths of microns in width, a very large number of MEMS switches can be provided on a single wafer.
MEMS switches have many advantages. Among other things, they are very small and inexpensive, depending on the configuration. Typically, the power consumption is also very minimal and their response time is extremely short. The complete sequence for closing or opening a MEMS switch can be as short as a few milliseconds.
Although previously existing MEMS actuators and switches were satisfactory to some degree, there was still a need to further improve their performance, reliability and manufacturability.